[NewPM][Sancov] Create the Sancov Pass after building the pipelines

[leonardchan]

Summary

We're running into linker errors from missing sancov sections:

ld.lld: error: relocation refers to a discarded section: __sancov_guards
>>> defined in user-arm64-ubsan-sancov-full.shlib/obj/third_party/ulib/scudo/scudo.wrappers_c.cc.o
>>> referenced by common.h:26 (../../zircon/third_party/ulib/scudo/common.h:26)
... many other references

I believe this is due to a pass in the default pipeline that somehow discards these sections. The ModuleSanitizerCoveragePass was initially added at the start f the pipeline. This now adds it to the end of the pipeline for optimized and unoptimized builds.

[chandlerc]

LGTM to fix folks broken by this.

That said, we should look for a way to test this in a follow up patch

cfe/trunk/lib/CodeGen/BackendUtil.cpp

if (CodeGenOpts.OptimizationLevel == 0) {
       // configure the pipeline.
       PassBuilder::OptimizationLevel Level = mapToLevel(CodeGenOpts);
 
       PB.registerPipelineStartEPCallback([](ModulePassManager &MPM) {
         MPM.addPass(createModuleToFunctionPassAdaptor(
             EntryExitInstrumenterPass(/*PostInlining=*/false)));
       });
 
-      if (CodeGenOpts.SanitizeCoverageType ||
-          CodeGenOpts.SanitizeCoverageIndirectCalls ||
-          CodeGenOpts.SanitizeCoverageTraceCmp) {
-        auto SancovOpts = getSancovOptsFromCGOpts(CodeGenOpts);
-        PB.registerPipelineStartEPCallback(
-            [SancovOpts](ModulePassManager &MPM) {
-              MPM.addPass(ModuleSanitizerCoveragePass(SancovOpts));
-            });
-      }
-
       // Register callbacks to schedule sanitizer passes at the appropriate part of
       // the pipeline.
       // FIXME: either handle asan/the remaining sanitizers or error out
       if (LangOpts.Sanitize.has(SanitizerKind::LocalBounds))
         PB.registerScalarOptimizerLateEPCallback(
             [](FunctionPassManager &FPM, PassBuilder::OptimizationLevel Level) {
               FPM.addPass(BoundsCheckingPass());
             });
if (CodeGenOpts.OptimizationLevel == 0) {
         MPM.addPass(CanonicalizeAliasesPass());
         MPM.addPass(NameAnonGlobalPass());
       } else {
         MPM = PB.buildPerModuleDefaultPipeline(Level,
                                                CodeGenOpts.DebugPassManager);
       }
     }
 
+    if (CodeGenOpts.SanitizeCoverageType ||
+        CodeGenOpts.SanitizeCoverageIndirectCalls ||
+        CodeGenOpts.SanitizeCoverageTraceCmp) {
+      auto SancovOpts = getSancovOptsFromCGOpts(CodeGenOpts);
+      MPM.addPass(ModuleSanitizerCoveragePass(SancovOpts));
+    }
+
     if (LangOpts.Sanitize.has(SanitizerKind::HWAddress)) {
       bool Recover = CodeGenOpts.SanitizeRecover.has(SanitizerKind::HWAddress);
       MPM.addPass(HWAddressSanitizerPass(
           /*CompileKernel=*/false, Recover));
     }
     if (LangOpts.Sanitize.has(SanitizerKind::KernelHWAddress)) {
       MPM.addPass(HWAddressSanitizerPass(
           /*CompileKernel=*/true, /*Recover=*/true));
     }
 
     if (CodeGenOpts.OptimizationLevel == 0) {
-      if (CodeGenOpts.SanitizeCoverageType ||
-          CodeGenOpts.SanitizeCoverageIndirectCalls ||
-          CodeGenOpts.SanitizeCoverageTraceCmp) {
-        auto SancovOpts = getSancovOptsFromCGOpts(CodeGenOpts);
-        MPM.addPass(ModuleSanitizerCoveragePass(SancovOpts));
-      }
-
       addSanitizersAtO0(MPM, TargetTriple, LangOpts, CodeGenOpts);
     }
   }
 
   // FIXME: We still use the legacy pass manager to do code generation. We
   // create that pass manager here and use it as needed below.
   legacy::PassManager CodeGenPasses;
   bool NeedCodeGen = false;